782 research outputs found
Typicality of pure states randomly sampled according to the Gaussian adjusted projected measure
Consider a mixed quantum mechanical state, describing a statistical ensemble
in terms of an arbitrary density operator of low purity, \tr\rho^2\ll
1, and yielding the ensemble averaged expectation value \tr(\rho A) for any
observable . Assuming that the given statistical ensemble is
generated by randomly sampling pure states according to the
corresponding so-called Gaussian adjusted projected measure Goldstein et
al., J. Stat. Phys. 125, 1197 (2006), the expectation value
is shown to be extremely close to the ensemble average \tr(\rho A) for the
overwhelming majority of pure states and any experimentally realistic
observable . In particular, such a `typicality' property holds whenever the
Hilbert space \hr of the system contains a high dimensional subspace
\hr_+\subset\hr with the property that all |\psi>\in\hr_+ are realized with
equal probability and all other |\psi> \in\hr are excluded.Comment: accepted for publication in J. Stat. Phy
The Brownian gyrator: a minimal heat engine on the nano-scale
A Brownian particle moving in the vicinity of a generic potential minimum
under the influence of dissipation and thermal noise from two different heat
baths is shown to act as a minimal heat engine, generating a systematic torque
onto the physical object at the origin of the potential and an opposite torque
onto the medium generating the dissipation.Comment: Phys. Rev. Lett., in pres
Anisotropic diffusion in square lattice potentials: giant enhancement and control
The unbiased thermal diffusion of an overdamped Brownian particle in a square
lattice potential is considered in the presence of an externally applied ac
driving. The resulting diffusion matrix exhibits two orthogonal eigenvectors
with eigenvalues , indicating anisotropic diffusion along a "fast"
and a "slow principal axis". For sufficiently small temperatures, may
become arbitrarily large and at the same time arbitrarily small. The
principal diffusion axis can be made to point into (almost) any direction by
varying either the driving amplitude or the coupling of the particle to the
potential, without changing any other property of the system or the driving.Comment: 7 pages, 7 figure
Suppression of thermally activated escape by heating
The problem of thermally activated escape over a potential barrier is solved
by means of path integrals for one-dimensional reaction dynamics with very
general time dependences. For a suitably chosen but still quite simple static
potential landscape, the net escape rate may be substantially reduced by
temporally increasing the temperature above its unperturbed constant level.Comment: 4 pages, 2 figure
Exploiting lattice potentials for sorting chiral particles
Several ways are demonstrated of how periodic potentials can be exploited for
sorting molecules or other small objects which only differ by their chirality.
With the help of a static bias force, the two chiral partners can be made to
move along orthogonal directions. Time-periodic external forces even lead to
motion into exactly opposite directions.Comment: 4 pages, 4 figure
Typical fast thermalization processes in closed many-body systems
Reimann P. Typical fast thermalization processes in closed many-body systems. NATURE COMMUNICATIONS. 2016;7(1): 10821.The lack of knowledge about the detailed many-particle motion on the microscopic scale is a key issue in any theoretical description of a macroscopic experiment. For systems at or close to thermal equilibrium, statistical mechanics provides a very successful general framework to cope with this problem. However, far from equilibrium, only very few quantitative and comparably universal results are known. Here a quantum mechanical prediction of this type is derived and verified against various experimental and numerical data from the literature. It quantitatively describes the entire temporal relaxation towards thermal equilibrium for a large class (in a mathematically precisely defined sense) of closed many-body systems, whose initial state may be arbitrarily far from equilibrium
Optimal evaluation of single-molecule force spectroscopy experiments
The forced rupture of single chemical bonds under external load is addressed.
A general framework is put forward to optimally utilize the experimentally
observed rupture force data for estimating the parameters of a theoretical
model. As an application we explore to what extent a distinction between
several recently proposed models is feasible on the basis of realistic
experimental data sets.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev.
Rolling and sliding of a nanorod between two planes: Tribological regimes and control of friction
The motion of a cylindrical crystalline nanoparticle sandwiched between two
crystalline planes, one stationary and the other pulled at a constant velocity
and pressed down by a normal load, is considered theoretically using a planar
model. The results of our model calculations show that, depending on load and
velocity, the nanoparticle can be either rolling or sliding. At sufficiently
high normal loads, several sliding states characterized by different friction
forces can coexist, corresponding to different orientations of the
nanoparticle, and allowing one to have low or high friction at the same pulling
velocity and normal load.Comment: 5 figure
- …